To download, install, and use Java™ packages more effectively on an iSeries™ server, see the following topics.
Packages with graphical user interfaces
Java programs used with graphical user interface (GUI) require the use of a presentation device with graphical display capabilities. For example, you can use a personal computer, technical workstation, or network computer. You can use Native Abstract Windowing Toolkit (NAWT) to provide your Java applications and servlets with the full capability of the Java 2 Software Development Kit (J2SDK), Standard Edition Abstract Windowing Toolkit (AWT) graphics functions. For more information, see Native Abstract Windowing Toolkit (NAWT).
Case sensitivity and integrated file system
Integrated file system provides file systems, which are both case-sensitive and those that are not with regard to file names. QOpenSys is an example of a case-sensitive file system within the integrated file system. Root, '/', is an example of a case-insensitive file system. For more information, see the Integrated file system topic.
Even though a JAR or class may be located in a case-insensitive file system, Java is still a case-sensitive language. While wrklnk '/home/Hello.class' and wrklnk '/home/hello.class' produce the same results, JAVA CLASS(Hello) and JAVA CLASS(hello) are calling different classes.
ZIP file handling and JAR file handling
ZIP files and JAR files contain a set of Java classes. When you use the Create Java Program (CRTJVAPGM) command on one of these files, the classes are verified, converted to an internal machine form, and if specified, transformed to iSeries machine code. You can treat ZIP files and JAR files like any other individual class file. When an internal machine form is associated with one of these files, it remains associated with the file. The internal machine form is used on future runs in place of the class file to improve performance. If you are unsure whether a current Java program is associated with your class file or JAR file, use the Display Java Program (DSPJVAPGM) command to display information about your Java program on your iSeries server.
In previous releases of the IBM® Developer Kit for Java, you had to recreate a Java program if you changed the JAR file or ZIP file in any way, because the attached Java program would become unusable. This is no longer true. In many cases, if you change a JAR file or ZIP file, the Java program is still valid and you do not have to recreate it. If partial changes are made, such as when a single class file is updated within a JAR file, you only need to recreate the affected class files that are within the JAR file.
Java programs remain attached to the JAR file after most typical changes to the JAR file. For example, these Java programs remain attached to the JAR file when:
If you access a JAR file in the integrated file system through iSeries Access for Windows® or from a mapped drive on a personal computer (PC), these Java programs remain attached to the JAR file when:
When a JAR file is changed or replaced, the Java program that is attached to it is no longer current.
There is one exception in which Java programs do not remain attached to the JAR file. The attached Java programs are destroyed if you use file transfer protocol (FTP) to replace the JAR file. For example, this occurs if you use the FTP put command to replace the JAR file.
See Java runtime performance for more detailed information about the performance characteristics of JAR files.
Java extensions framework
In J2SDK, extensions are packages of Java classes that you can use to extend the functionality of the core platform. An extension or application is packaged in one or more JAR files. The extension mechanism allows the Java virtual machine to use the extension classes in the same way that the virtual machine uses the system classes. The extension mechanism also provides a way for you to retrieve extensions from specified URLs when they are not already installed in the J2SDK or Java 2 Runtime Environment, Standard Edition.
See Install extensions for the IBM Developer Kit for Java for information on installing extensions.